The ultimate goal of the modern scientific technology development is to improve the quality of human life. Especially, in the fields of biotechnology and environmental engineering, various researches have been actively conducted to predict a disease or diagnose a disease at an early stage prior to starting the treatment and to efficiently control various kinds of problems that may directly affect the human life span.
As examples of such research trend, the research and developments have been made for a human body biomarker for detecting a harmful substance or diagnosing a disease, and a super-microscopic precision sensor system for detecting the presence of a sensing-target material such as a pathogenic organism, or the occurrence of a certain biochemical reaction in a fast and simple manner. When a biochemical substance and a harmful pollutant to be sensed, which exist in air, aquatic environment or the human body, are present in a very low concentration, there are many drawbacks to be overcome in order to analyze them by a conventional analysis method. That is, a high-cost and large-scale analyzing apparatus is required for extraction, concentration and analysis of a sample and it takes a great amount of time for pre-treating a sample. In order to analyze the sensing-target material on a real-time basis without having to perform the sample pre-process such as the sample extraction and concentration, the sensitivity of a sensor device used in the analysis needs to be high enough to detect a mass at a single-molecule level.
As one of such sensors, a microcantilever integrated with a piezoelectric driving component can be self-driven by an AC electric field and can quickly read a great change in an AC signal caused by a piezoelectric effect at a resonant frequency point through an electric measurement. Research reports related to this have been already reported by many other researchers, including the patent applications and the journals filed and published by the present inventors' research group.
In an actual application for detecting a sensing-target material, a microcantilever resonator sensor operated with a resonant frequency using a piezoelectric mechanism or another driving principle outputs a sensing signal in the form of a resonant frequency shift of a cantilever with respect to a mass change on a cantilever surface that occurs during a sensing process, and analyzes it to give a result. To implement a wider range of application and a more accurate analysis, it is desirable to use an array-type device having an array of a plurality of cantilevers rather than to use a single cantilever. Meanwhile, the resonant frequency of the cantilever decreases or increases due to a change in the surface stress as well as due to a change in the surface mass during the sensing process. However, when a single cantilever or an array-type device having an array of a plurality of same-sized cantilevers is used, a mass loading effect and a surface stress change effect occurring during the sensing process cannot be distinguished when a resonant frequency change as a sensing signal is analyzed. Although the degree of mechanical bending of the cantilever due to the surface stress change can be measured and analyzed by an optical method, it is difficult to discriminately analyze the mass loading effect and the surface stress change effect in case of using the resonant frequency shift as a primary sensing signal, since the mass loading effect and the surface stress effect are simultaneously exerted.